This issue affect any apps on Play Store, with stock launchers (LG, Google, Samsung, Motorola, etc) on Android 4.1 and above. There is a known bug in OS / stock launchers, that causes added widgets to disappear from stock launchers when the related app is updated. Other third party (non-stock) launchers are not affected by this bug or have never been reported to suffer from this!

A possible workaround is to kill the launcher when that happens. It works on LG G4. Please let me know if it works on others, I'll update this page!

There is no other workaround to this issue because of the way Android OS updates the app. The larger the app the longer it will take the OS to update it. During the whole update process the app is made unavailable, and if a launcher decides to update it, it will likely dismiss it. Only the launchers can implement a workaround.

Here are things that can help prevent losing widgets:

- Move apps to internal storage, the update process will be faster reducing the chance of being affected

- Use a third-party launcher, most appear to have implemented a workaround.

- Disable affected apps auto-update.

To make this less frustrating, please save your widget configurations so you can apply them again quickly when adding back your widgets.

You can find more information here where other devs/users have reported the same issue, possibly affecting any paid apps: